This relates generally to imaging sensors, and more particularly, to imaging sensors with optical cavity image pixels.
Modern electronic devices such a cellular telephones, cameras, and computers often use digital image sensors. Imagers (i.e., image sensors) may be formed from a two-dimensional array of image sensing pixels. Each pixel may include a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical charges. Conventional image pixel arrays include frontside illuminated image pixels or backside illuminated image pixels. Image pixels are fabricated on a semiconductor substrate using complementary metal-oxide-semiconductor (CMOS) technology or charge-coupled device (CCD) technology. The image sensors may include photodiodes and other operational circuitry such as transistors formed in a front surface of the substrate. In a configuration that includes frontside illuminated image pixels, a dielectric stack is formed on the front surface of the substrate directly on top of the photodiodes. The dielectric stack includes metal routing lines and metal vias formed in dielectric material. Image light passes through the dielectric stack to the photodiodes. In a configuration that includes backside illuminated image pixels, the photodiodes receive image light through the backside of the semiconductor substrate so that the light does not pass through the dielectric stack.
However, in conventional frontside and backside illuminated image pixels, the image light only makes a single pass through the semiconductor substrate. For this reason, some of the light can pass through the photodiode without being converted into detectable electric charge. This undetected light can negatively affect the quantum efficiency of the pixel and can limit the performance of the device, particularly in low-light imaging operations. Additionally, some of the light may be scattered or diffracted into neighboring pixels and/or photon-generated charge may diffuse into neighboring pixels thus creating pixel crosstalk and further degrading the performance.
It would therefore be desirable to be able to provide improved image pixels for imaging devices.